1. Field of the Invention
The present invention relates to a matrix substrate, a liquid-crystal device for displaying images and letters by use of the matrix substrate and liquid crystal, and a display device incorporating the liquid-crystal device. More particularly, the invention concerns a liquid-crystal device and a display device characterized by a horizontal driving circuit and a vertical driving circuit for driving liquid-crystal elements.
2. Related Background Art
As the world moves into the multimedia age nowadays, devices for communications by image information are increasing their importance. Among others, liquid-crystal display devices are drawing attention because of their small thicknesses and low consumption power and have grown to one of basic industries, as comparable to semiconductors. The liquid-crystal display devices are now used mainly in 10-inch size notebook personal computers. It is to be expected that the liquid-crystal display devices of larger screen sizes will be used not only for the personal computers, but also for workstations and home-use televisions in the future. With increase in the screen size, however, manufacturing equipment will become more expensive and electrically severe characteristics will be demanded for driving the large screen. Therefore, with increase in the screen size, the manufacturing cost will rapidly increase in proportion to the square to the cube of the size.
Under such circumstances, attention is focused recently on a projection method for fabricating a compact liquid-crystal display panel and optically enlarging a liquid-crystal image to display it. The reason is that the decrease of size can improve the characteristics and also decrease the cost, similar to the scaling law that the performance and cost are improved with compactification of semiconductor. From these points, when the liquid-crystal display panel is of a so-called active matrix type wherein a TFT (Thin Film Transistor) is provided for each pixel, compact TFTs having sufficient driving force are necessary and a trend is to move from amorphous Si TFTs to polycrystalline Si TFTs. Video signals of the resolution level according to the NTSC standards adopted in the ordinary televisions do not require so quick processing.
Therefore, the liquid-crystal display devices can be fabricated in the integral structure incorporating the display area and peripheral driving circuits by making not only the TFTs, but also even the peripheral driving circuits such as shift registers or decoders of polycrystalline Si. However, since polycrystalline Si is inferior to monocrystalline Si, in order to realize high-definition televisions of a higher resolution level than in the NTSC standards or displays of the XGA (extended Graphics Array) or SXGA (Super extended Graphics Array) class in the resolution standards of computer, a plurality of separate shift registers must be provided. In this case, there appears noise called ghost in display areas corresponding to borders of separation and desires to solve the problem exist in this field.
On the other hand, attention is also focused on the display devices of the monocrystalline Si substrate achieving extremely high driving force, rather than the display devices of the integral structure of polycrystalline Si. In this case, the driving force of transistor by the peripheral driving circuits is sufficient and thus the separate driving as described above is not necessary. This solves the problem of the noise.
With use of either of these polycrystalline Si and monocrystalline Si, a reflection type liquid-crystal device can be provided in such a way that reflection type liquid-crystal elements are formed by connecting the drains of TFTs with reflecting electrodes and interposing the liquid crystal between the reflecting electrodes and a transparent common electrode and that horizontal and vertical shift registers for scanning of the liquid-crystal elements are formed on the same semiconductor substrate.
Under such circumstances, a driving circuit for liquid-crystal device that can decrease the consumption power of active matrix liquid-crystal device was proposed as disclosed in Japanese Laid-open Patent Application No. 59-133590 (JPA 59-133590). This JPA 59-133590 discloses the driving circuit wherein a signal line driving circuit for selection of signal line is composed of plural shift registers and wherein a selecting circuit for selecting and applying two clock signals is provided for each shift register and describes use of dynamic shift registers as the shift registers.
It is described that this invention can decrease the consumption power by supplying low-frequency clocks to the most shift registers and can expectedly achieve increase of yield by use of the dynamic shift registers.
However, when the signal line driving circuit is constructed of the plurality of separate shift registers, the fact is that this arrangement is not completely free of occurrence and instability of the noise called the ghost discussed above. The JPA 59-133590 omits investigation on configurations of the both signal line driving circuit and scanning line driving circuit for liquid-crystal devices ready for high resolutions and many pixels, based on total consideration of the area of a chip in which the pixels and driving circuits are made, the consumption power, and reliability.